As a hard film, an amorphous carbon film is known. The amorphous carbon has an intermediate merged structure between that of diamond and that of graphite, and is also referred to as hard amorphous carbon, indefinite carbon, hard indefinite carbon, i-carbon, diamond-form carbon, diamond-like carbon (DLC), or the like. The amorphous carbon (which may be hereinafter referred to as DLC) is, as with diamond, high in hardness, and is excellent in wear resistance, solid lubricity, thermal conductivity, and chemical stability. For this reason, amorphous carbon has come into use as each protective film of various components such as sliding members, dies, cutting tools, wear-resistant mechanical components, polishing materials, and magnetic/optical components. Amorphous carbon has features of being chemically inactive and having a low reactivity with nonferrous metals, and has come into practical use as a coating film of a cutting tool for aluminum or copper materials particularly taking advantage of these features.
The methods for manufacturing the amorphous carbon film are largely divided into two kinds of a PVD (Physical Vapor Deposition) method and a CVD (Chemical Vapor Deposition) method. With deposition by the CVD method, as advantages, mention may be made of high deposition rate and coatability on a substance in complicated shape. However, with deposition by the CVD method, the amorphous carbon film is manufactured by decomposing a hydrocarbon gas. For this reason, the amount of hydrogen mixed into the amorphous carbon film is large. Thus, it is unfavorably difficult to enhance the hardness of the amorphous carbon film as expected.
On the other hand, with deposition by the PVD method, by not using a hydrocarbon gas, or setting the amount of hydrocarbon gas to be introduced during deposition at a trace amount, it is possible to manufacture an amorphous carbon film not containing hydrogen or having a low hydrogen content.
There is proposed a technology of forming a nitrogen-containing amorphous carbon-type film using the methods, and improving the characteristics thereof than those of an amorphous carbon film. For example, Patent Literature 1 proposes the following technology: on the assumption that a sliding member is used under dry environment, a nitrogen-containing amorphous carbon-type film is formed on the sliding surface of the member, and the atmosphere in the periphery of the sliding part during sliding is set to be a nitrogen atmosphere, thereby preventing oxidation of carbon in the film.
Further, for example, Patent Literature 2 proposes the following technology: a nitrogen-containing amorphous carbon-type film and a layer including a IVa group element in the periodic table, or the like are stacked, or the IVa group element in the periodic table or the like is dispersed in the nitrogen-containing amorphous carbon-type film, thereby to reduce the coefficient of friction.